South Carolina Sen. Lindsey Graham on Tuesday sharply criticized Donald Trump's insinuations that President Barack Obama knew more about or sympathizes with the attack in Orlando, Florida, as "highly offensive."

Federal officials are investigating Sunday's mass shooting at a gay nightclub Sunday that left 49 victims dead as an act of terrorism. The gunman, 29 year-old Omar Mateen reportedly pledged allegiance to the Islamic State terror group, also known as ISIS.

Trump, the presumptive Republican presidential nominee, said in a Monday interview with Fox News, "Look, we're led by a man that either is, is not tough, not smart, or he's got something else in mind."

"He loves his country, President Obama, but he is doing a very poor job at defending it," Graham said. "Mr. Trump seems to be suggesting that the president is one of them. I find it highly offensive. I find that whole line of reasoning way off base."

Graham also said that Trump's reaction to the Orlando attack proved the billionaire mogul does not have the judgment or temperament to be commander in chief. In a tweet after the attack, Trump said he appreciated the congratulations for being right about radical Islamic terrorism. He also doubled down on his call to temporarily ban foreign Muslims from entering the U.S.

Sen. Susan Collins of Maine said his comments were "inappropriate" with people in Orlando still mourning. Wisconsin Sen. Ron Johnson criticized Trump on Monday for renewing his call for a ban on Muslim immigration.

Sen. Kelly Ayotte of New Hampshire said that after reviewing excerpts of Trump's foreign policy speech Monday in her home state, she continued to disagree with the presumptive nominee about imposing religious tests for entering the United States.